The present invention relates to an ion transport barrier, particularly one used for an ion transport device such as one for generating a high-purity acid, base, or salt or for a suppressor in an ion chromatography system.
In liquid chromatography, a liquid sample containing a number of components to be separated is directed through a chromatography separator, typically an ion exchange resin bed. The components are separated on elution from the bed in a solution of eluent. One form of liquid chromatography is referred to as ion chromatography. In this known technique, ions to be detected in the sample, consisting of ions in an aqueous solution, are separated in a chromatography separator, such as a chromatography column, using an eluent containing an acid or a base and, thereafter, sent to a suppressor, followed by detection, typically by an electrical conductivity detector. In the suppressor, the electrical conductivity of the electrolyte is suppressed but not that of the separated ions, so that the latter may be detected by the conductivity detector. One such suppressor, disclosed in U.S. Pat. No. 6,325,976, is continuous and electrolytic. Suppression is in a packed bed of ion exchange resin. Other suppressors are disclosed in U.S. Pat. Nos. 4,999,098, 4,500,430, 4,647,380 and 5,352,360. There, the suppressor is in the form of a membrane suppressor in which a regenerant solution flows on one side of an ion exchange membrane and the sample stream flows on the other side. Suppression occurs by transport of electrolyte ions of opposite charge to the sample ions in the eluent across the membrane and into the regenerant solution. Thus, the suppressor serves as an ion transport apparatus.
A convenient source of high-purity acid, base, or salt for use as an eluent for liquid chromatography and, particularly, for ion chromatography is disclosed in U.S. Pat. Nos. 5,045,204 and 6,225,129. As disclosed, for the generation of a base or acid, a cation or anion source is disposed in a flowing or non-flowing cation or anion source reservoir. An aqueous liquid flows through a base- or acid-generation chamber separated from the source reservoir by an ion exchange barrier, in the form of an ion exchange membrane, substantially blocking liquid flow across it while providing a cation or anion transport bridge. Electrical potential is applied to electrolytically generate hydroxide or hydronium ions in the base or acid generation chamber. Thus, like the suppressor of U.S. Pat. No. 5,352,360, the acid or base generation apparatus of U.S. Pat. No. 6,225,129 or 5,045,204 or devices described in US Patent Application 20060211125 are ion transport apparatus in which ions are transported across an ion exchange membrane.
There would be an advantage for providing a form of ion transport barrier in such prior art ion transport apparatus which has improvements over the ion exchange membrane of such ion transport apparatus.